Question

背景：我正在尝试使用Qt Graphics View框架在python中制作VR演示，该框架允许自定义呈现的GUI。我可以选择包装Qt的两个不同的python模块：PyQt5和PySide2。不幸的是，每个模块似乎都在Graphics View Framework中缺少了不同的关键要素。

PyQt5似乎缺少QGraphicsSceneMouseEvent的构造函数，而从VR控制器手势创建合成鼠标事件则需要该构造函数。这个简短的PyQt5程序...

from PyQt5.QtCore import QEvent, QPointF, Qt
from PyQt5.QtGui import QMouseEvent
from PyQt5.QtWidgets import QGraphicsSceneMouseEvent
from PyQt5.QtGui import QOpenGLPaintDevice  # No problem for PyQt5

pos = QPointF(20, 20)
event1 = QMouseEvent(QEvent.MouseMove, pos, Qt.LeftButton, Qt.LeftButton, Qt.NoModifier)
device = QOpenGLPaintDevice(100, 100)

# Problem: TypeError: PyQt5.QtWidgets.QGraphicsSceneMouseEvent cannot be instantiated or sub-classed
event2 = QGraphicsSceneMouseEvent(QEvent.GraphicsSceneMouseMove)

...结果为TypeError: PyQt5.QtWidgets.QGraphicsSceneMouseEvent cannot be instantiated or sub-classed

看似好消息是，替代Qt绑定PySide2模块可以构造一个QGraphicsSceneMouseEvent而不会引起抱怨。但是PySide2缺少QOpenGLPaintDevice类，我实际上需要绘制它。这个非常相似的程序，使用PySide2 ...

from PySide2.QtCore import QEvent, QPointF, Qt
from PySide2.QtGui import QMouseEvent
from PySide2.QtWidgets import QGraphicsSceneMouseEvent

pos = QPointF(20, 20)
event1 = QMouseEvent(QEvent.MouseMove, pos, Qt.LeftButton, Qt.LeftButton, Qt.NoModifier)
event2 = QGraphicsSceneMouseEvent(QEvent.GraphicsSceneMouseMove)  # No Problem for PySide2

from PySide2.QtGui import QOpenGLPaintDevice  # Problem: PySide2 does not have this class
device = QOpenGLPaintDevice(100, 100)

得出ImportError: cannot import name 'QOpenGLPaintDevice'

我不确定有人能成功使用python的Qt Graphics View框架。如果没有，我想成为第一个。

Answer 1

在我看来，并不是PyQt5中未启用QGraphicsSceneMouseEvent的错误，而是PySide2中已启用的错误，因为如果您查看the docs，就会发现QGraphicsSceneMouseEvent没有公共构造函数

如果要在Qt Graphics Framework中模拟鼠标移动，则必须将QMouseEvent发送到QGraphicsView的viewport()。

在下面的示例中，我演示如何通过使用QMouseEvent模拟鼠标来移动项目：

from functools import partial
from PySide2 import QtCore, QtGui, QtWidgets
# from PyQt5 import QtCore, QtGui, QtWidgets


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.m_scene = QtWidgets.QGraphicsScene(QtCore.QRectF(0, 0, 400, 400), self)
        self.m_graphicsview = QtWidgets.QGraphicsView(self.m_scene)
        self.setCentralWidget(self.m_graphicsview)
        self.resize(640, 480)

        self.m_item = QtWidgets.QGraphicsRectItem(QtCore.QRectF(-50, -50, 100, 100))
        self.m_item.setFlags(
            self.m_item.flags() | QtWidgets.QGraphicsItem.ItemIsMovable
        )
        self.m_item.setBrush(QtGui.QColor("salmon"))
        self.m_item.setPos(100, 100)
        self.m_scene.addItem(self.m_item)

        QtCore.QTimer.singleShot(1000, self.emulate_move_item)

    def emulate_move_item(self):
        sp = self.m_item.mapToScene(self.m_item.boundingRect().center())
        lp = self.m_graphicsview.mapFromScene(sp)
        end_pos = lp + QtCore.QPoint(100, 100)

        self.press(lp)

        animation = QtCore.QVariantAnimation(
            self,
            startValue=lp,
            endValue=end_pos
        )
        animation.valueChanged.connect(self.moveTo)
        animation.finished.connect(partial(self.release, end_pos))
        animation.start(QtCore.QAbstractAnimation.DeleteWhenStopped)

    def press(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseButtonPress,
            pos,
            self.m_graphicsview.mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)

    def moveTo(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseMove,
            pos,
            self.m_graphicsview.viewport().mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)

    def release(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseButtonRelease,
            pos,
            self.m_graphicsview.viewport().mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)

    def double_click(self, pos):
        event = QtGui.QMouseEvent(
            QtCore.QEvent.MouseButtonDblClick,
            pos,
            self.m_graphicsview.viewport().mapToGlobal(pos),
            QtCore.Qt.LeftButton,
            QtCore.Qt.LeftButton,
            QtCore.Qt.NoModifier,
        )
        QtCore.QCoreApplication.postEvent(self.m_graphicsview.viewport(), event)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())

结论：

不能在python中启用QGraphicsSceneMouseEvent构造函数，因为在C ++中Qt的公共API中无法访问它。因此PyQt5的行为是正确的，但是PySide2有一个错误。
PySide2没有实现QOpenGLPaintDevice类是一个可能的错误。

如何从python使用Qt的“图形视图”框架？

1 个答案: